To determine the effects of cysteine supplementation of parenteral nutrition regimens of (LBW) infants on the plasm concentrations of cyst(e)ine, taurine and GSH, nitrogen retention and leucine turnover and the rates of synthesis of taurine and glutathione (from cysteine).Subjects enrolled will be selected from among the patients in the Neonatal Nursery of Ben Taub General Hospital deemed by the medical staff to require parenteral nutrition as the sole source of nutrients for at least five days.